Fix unclosed file warnings

Tests/test_file_bufrstub.py

@@ -56,6 +56,7 @@ def test_handler(tmp_path):
 
         def load(self, im):
             self.loaded = True
+            im.fp.close()
             return Image.new("RGB", (1, 1))
 
         def save(self, im, fp, filename):

Tests/test_file_fits.py

@@ -60,6 +60,7 @@ def test_stub_deprecated():
 
         def load(self, im):
             self.loaded = True
+            im.fp.close()
             return Image.new("RGB", (1, 1))
 
     handler = Handler()

Tests/test_file_gribstub.py

@@ -56,6 +56,7 @@ def test_handler(tmp_path):
 
         def load(self, im):
             self.loaded = True
+            im.fp.close()
             return Image.new("RGB", (1, 1))
 
         def save(self, im, fp, filename):

Tests/test_file_hdf5stub.py

@@ -57,6 +57,7 @@ def test_handler(tmp_path):
 
         def load(self, im):
             self.loaded = True
+            im.fp.close()
             return Image.new("RGB", (1, 1))
 
         def save(self, im, fp, filename):

Tests/test_imageshow.py

@@ -55,7 +55,7 @@ def test_show_without_viewers():
     viewers = ImageShow._viewers
     ImageShow._viewers = []
 
-    im = hopper()
+    with hopper() as im:
         assert not ImageShow.show(im)
 
     ImageShow._viewers = viewers